Our laboratory has had a long standing interest in the potential of anti- idiotypic antibodies to serve as molecular mimics of nominal antigens. In pursuit of this, we have raised and fully characterized a number of monoclonal anti-ids against a monoclonal idiotype which recognizes the protective a determinant epitope of hepatitis B surface antigen (the outer envelope protein of the hepatitis B virus). The anti-id designated 2F10 has been shown to functionally mimic HBsAg and generate specific B and T cell responses in vivo and in vitro. A 15 amino acid region of the heavy chain hypervariable region of the anti-id that has partial residue homology with sequences of the a determinant epitopes of HBsAg has been identified. Further a synthetic 15mer peptide derived from the anti-id sequence can duplicate the B and T cell stimulatory activity of the anti-id and the antigen that it mimics, HBsAg. An important aspect of these studies was based on the observation that the HBsAg non-responder B10.M (H-2~ strain made an a determinant anti-HBs antibody response following immunization with the anti-id 2F10. These results are important in the context of the very extensive and elegant studies that have established that HBsAg shows MHClinked immune responses in both man and mouse. A number of studies have helped to consolidate the view that only a very limited number of key residues are essential for effective binding of a peptide to specific Class I and II products. We have begun to explore the possibility that the inertness of HBsAg in B10.M mice (and perhaps even in Hepatitis B vaccine non-responders and HBV carriers) could be the consequence of possible defects in antigen presentation specific to HBsAg and that peptides derived from the anti-id are able to overcome this defect. The specific aims of this proposal are: (1) A study of MHC-peptide interactions---a basis for non-responsiveness to HBsAg observed in B10.M mice, human HBV carriers and HBsAg vaccine non~responders: (2) An analysis of the amino acid residues of the anti-id, important for peptide-MHC interactions and T cell recognition. This will be achieved by using a panel of single amino acid-substitution analogues of the anti-id sequence. (3) Characterization of B and T cell epitopes contained within the anti-id derived 15mer peptide. This will be achieved using appropriately truncated synthetic peptides. (4) The generation of additional human T cell clones from different donors including HBV carriers and vaccine non-responders and continuation of the complete analysis of the clones that have already been established. Since the techniques that will be used for this proposal are well in hand, and we have some promising results from our preliminary experiments, we believe that the project we have submitted is a feasible one and well within our expertise.